While ID (i.e., ID75, ID90, etc.) tickets are usually valid for 90 days only, ZED tickets which are valid for 6 months.

What I find interesting, though, is your last comment "the airline i work for only allows 2 interline requests a year".

In the past ID90 travel was generally limited to 1 ticket per year on a bilateral basis, however, many US carriers have, over the years, bilaterally increased the allotment to 6 (in some cases unlmited). ZED tickets are unlimited.

I'd be curious to learn what airline you work with.